The present invention relates to a dispensing apparatus for dispensing precisely measured doses of dry and/or powdery bulk materialsxe2x80x94toxic substances in particularxe2x80x94into small containers that are placed on a balance. The bulk materials are dispensed from a reservoir container by means of a conveying and delivering device.
Dispensing apparatus for dry and/or powdery bulk materials such as, e.g., color dyes, are known and used in practice. A device of this kind is described in EP-A 0 406 164, consisting of a dispensing container with a substantially closable outlet at its underside and a balance onto which the bulk material can be dispensed by a conveyor means. The closure is provided by a tapered valve body, wide at the bottom and narrow at the top, that can be moved downward in the vertical direction. The tapered valve body, which rotates when in its open state, is equipped with means for advancing the bulk material towards the outlet opening.
The device of the foregoing description is not well suited for dispensing bulk material into containers that have openings of narrow cross-section. The widening taper of the valve body towards the outlet opening, combined with the effect of the rotation, imparts a radial, horizontal velocity component to the material particles as they leave the outlet, thereby causing the material to be scattered over a range that can go outside the cross-section of an even relatively wide opening of a receiving container. Consequently, it is not always possible to avoid the loss of bulk material, or even the contamination of the surrounding area, when dispensing material into containers with a narrower opening than the ring-shaped outlet gap. Possibly, this may add a costly clean-up step to the dispensation process.
A costly cleaning processxe2x80x94particularly when toxic powders are dispensedxe2x80x94can also be necessitated by the aforementioned dispensing apparatus itself, particularly in the area of the valve and the outlet, but also in the dispensing container itself, given that a driving shaft runs inside it. Because of the driving shaft, the dispensing container of the known device has to be of a specialized, expensive design that is specifically adapted to the purpose of dispensing doses of the container contents. The arrangement of the shaft can also interfere with the process of filling the dispensing container before the actual dispensing operation is started.
Therefore, the objective of the invention is to provide a device for dispensing dosage quantities of bulk material in a directed stream without spillage losses into containers with openings of narrow cross-section and to meet the additional requirements that the device be efficient to clean and easy to handle.
The dispensing apparatus for bulk materials, primarily substances of powdery consistency, comprises a balance receiving the material that is to be apportioned into dosage quantities, a reservoir container, and a cover that closes off the underside of the reservoir container. Integrated in the cover is a conveying and delivering device. The conveying and delivering device contains a vertically movable and rotatable conveyor body that can substantially close the outlet from which the bulk material is dispensed. In its ring-shaped lower part, the conveyor body has a narrowing taper towards the bottom end. The tapered part of the conveyor body reaches into a correspondingly tapered recess of the cover. The outlet passage, which preferably has a slightly conical shape that widens towards the downside, is arranged to the side of the center of the conveyor body. The outlet is located in the ring-shaped path swept by the conveyor body and produces a directionally targeted and locally concentrated delivery of bulk material.
The advantageous results of the concentrated and directionally focussed material delivery are that the balance carrying the receiving container will not be contaminated by spilled material and the weighing result will not be falsified by material particles that miss the receiving container but still land on the weighing pan.
By a coordinated variation of several variable parameters such as the rate of rotation of the conveyor body, or its vertical position which controls the aperture cross-section of the passage from the reservoir, it is possible to adapt the delivery rate to the requirements of the dispensation process. Thus, it is possible to release bulk material at a fast rate at the beginning of a dispensation and to progressively slow down the delivery rate towards the end of the process.
By simplifying the configuration of the reservoir container and by integrating the conveying and delivering device in the cover of the reservoir container, the invention facilitates handling procedures, e.g., in exchanging the reservoir container against another reservoir container with bulk material to be dispensed. Due to the use of low-cost materials, e.g., polymers, for the cover-integrated conveying and delivering device, the cleaning procedure is simplifiedxe2x80x94particularly when working with toxic powdersxe2x80x94because the entire cover unit including the conveying and delivering device is used for only a single filling of the reservoir container (the latter also serving as storage container with the outlet opening closed). After the reservoir container has been completely emptied as a result of dispensing the contents, the entire unit can be safely disposed.
In a preferred embodiment of the invention, the conveyor body is shaped like an upright cone tapering to an apex on the central axis of the ring-shaped path. The cone has openings for the passage of the bulk material to be dispensed. The spokes delimiting the openings can be designed as means for scooping up and taking along the bulk material and can in particular have the shape of shovels.
In further advantageous embodiments of the invention, the ring-shaped bottom portion of the conveyor body is equipped with pick-up means for taking along the particles of the bulk material. The pick-up means can have the form of conveyor slits running transverse to the circumference of the ring, or conveyor ledges, or a groove in the circumference of the ring. It is also possible to configure the conveyor body in two parts, one of which is the pick-up means, to be placed over the main part and preferably configured as an exchangeable element. The concept of a separately installed part makes it possible to manufacture it from a material and in a shape that is specifically adapted to the consistency of the bulk material. A soft polymer is suitable, for example silicone. The pick-up means can in this case have the form of fingers that are arranged transverse to the circumference of the ring, or as brushes. Providing different conveyor bodies has the advantage that the device can be adapted to the consistency of the bulk material that is to be dispensed (freely pourable, sticky, etc.). This idea can be implemented in practice so that the profile of the ring-shaped underside of the conveyor body is essentially the same for all of the different design variations, and therefore the ring-shaped conveyor channel in the cover can have the same shape for all variations, meaning that only a single version of the parts would be required. However, it is also possible to adapt the profile of the conveyor channel to the requirements of each specific type of pick-up means in order to optimize the outflow rate. A particularly advantageous embodiment for directing bulk material to the outlet opening has a non-centric conveyor channel of variable depth and width, narrowing down towards the outlet opening.
In the case of particularly clingy powder substances, the invention provides for a wiper device in the area of the outlet opening. Preferably, the position of the wiper device is coupled to the height setting of the conveyor body, so that the wiper device stays at a set distance and remains fully effective if the axial position of the conveyor body is changed. Corresponding to the shape of the pick-up means at the underside of the conveyor body, e.g., slits or ledges running transverse to the circumference of the ring, or a groove in the circumference of the ring, the wiper device can be configured either with a concave recess or with a finger that stands out and reaches into a groove. An embodiment with several fingers arranged like a comb is also possible, e.g., if there is a plurality of conveyor grooves at the underside of the conveyor body.
In a particularly advantageous embodiment of the invention, the shaft that holds the conveyor body protrudes from the center of the underside of the cover of the dispensing apparatus and is driven by a motor located on the opposite side from the outlet opening.
For bulk materials of a less free-flowing, pourable consistency, a preferred embodiment of the invention has stirring means inside the reservoir container as well as a vibrator device that can be arranged on the outside of the reservoir container.
It is self-evident, that the dosage-dispensing process performed by the inventive device can also be automated through an arrangement where a computer/controller unit (which can be integrated in the balance) controls the dispensing process and stops the dispensation of material when the target weight has been reached. The automated apparatus can further include a conveyor device that brings a new, empty dosage-portion container to the balance after the preceding container has been filled to the set target weight.